1. Field
Apparatuses consistent with exemplary embodiments relate to a membrane filtration system for treating wastewater, and more particularly to a membrane filtration system having increased filtration and nutrient removal performance as a result of employing the repeated back and forth motion (hereinafter referred to as “reciprocating motion” or “reciprocation”) of a submerged membrane instead of membrane scouring that is used in a submerged membrane filtration system of the related art.
2. Description of the Related Art
Several examples of membrane filtration systems utilize membrane filtration processes to remove contaminants from wastewater. Several modified membrane processes can be used alone or in series for improved removal of contaminants in membrane filtration. Known membrane filtration systems also use low-pressure microfiltration (MF) or ultrafiltration (UF) membranes as a physical barrier for complete solid-liquid separation. The membranes are typically installed in a filtration tank. Membrane air scouring is of utmost importance in submerged membrane filtration operation to prevent severe and rapid membrane fouling. By way of these known techniques, membrane filtration systems can achieve secondary and tertiary wastewater treatment.
One advantage of known membrane filtration systems is the direct introduction of tertiary quality effluent to the treatment of domestic or industrial wastewater. Another reason for the growing interest in membrane filtration technology is its smaller footprint compared to conventional treatment processes. For example, using the membrane filtration systems, a treatment plant could potentially double the capacity of the treatment plant without increasing the overall footprint of the plant. Membrane filtration technology is not only limited to domestic wastewater, but the membrane filtration technology can also be applied to treat industrial wastewater for reuse.
An example of a membrane filtration system is disclosed in U.S. Pat. No. 4,867,883 to Daigger. The Daigger reference discloses a high-rate biological wastewater treatment process for removing organic matter, phosphorus and nitrogen nutrients from municipal wastewater. Another membrane filtration system is disclosed is U.S. Pat. No. 8,287,733 to Nick et al. The Nick reference discloses a system utilizing first and second anoxic basins and first and second aerobic basins and also discloses the use of a membrane chamber for housing a plurality of membrane tanks.
One common drawback of known membrane filtration systems is membrane fouling. The membrane fouling occurs when soluble and particulate materials accumulate on the membrane surface. When the membrane fouling occurs, there is either a marked decline in permeate passing through the membrane or an increase in the transmembrane pressure. In either event, the result is a dramatic reduction in system performance. Membrane fouling is especially problematic in membrane filtration systems given that the membrane filtration systems generally operate with higher mixed liquor suspended solids (MLSS).
One solution to membrane fouling is air scouring. Vigorous air scouring allows for stable flux operation without rapid and permanent fouling and especially cake layer buildup. Given the higher MLSS concentrations at which membrane filtration systems operate, frequent maintenance cleanings and out-of-tank cleanings are also important to maintain membrane performance in terms of fouling and permeability. Air scouring is not optimal as it is energy intensive. In membrane filtration systems, energy consumption is considerably high due to the additional air scouring for the membrane. In addition, because air scouring is a process of vigorously blowing air, it is unsuitable for combination with processing units suitable for oxygen-deficient conditions such as anoxic or anaerobic conditions or low-speed agitation conditions, and thus there are many limits to the use of air scouring in various applications.